The possible roles of parathyroid calcium binding protein (P-CaBP) and calmodulin in the calcium-regulatory mechanism of parathyroid tissue will be incubated in vitro. The secretory response of the explants to alteration in the extracellular calcium concentration will be compared to the amounts of P-CaBP present in the tissue. P-CaBP will be isolated from human parathyroid tissue using gel filtration and isoelectric focusing. Antisera will be raised against the human P-CaBP and used to determine its tissue specificity by radioimmunoassay and its subcellular localization in parathyroid tissue by ultrastructural immunohistological procedures. Using radiolabeled P-CaBP and various fractionation procedures in the presence and absence of calcium, we will attempt to identify the cellular components with which P-CaBP interacts. Employing the activation of calmodulin-depleted phosphodiesterase as an assay for calmodulin parathyroid extracts will be assayed for calmodulin content. If parathyroid tissue can be demonstrated to contain calmodulin, using 125I-labeled calmodulin, selective fractionation procedures, and affinity chromatography we will attempt to identify and characterize the calmodulin-binding proteins present in this tissue. In addition, using both the phosphodiesterase enzymatic assay and electrophoretic separation procedures, the calmodulin content of normal and abnormal human parathyroid tissues will be determined. The effects of calcium, alone and in combination with P-CaBP and calmodulin, on adenylate cyclase and phosphodiesterase activities will be studied using normal dog parathyroid tissue. The different species of phosphodiesterases will be separated using ion-exchange chromatography and individually characterized.